This invention relates to an ignition coil for supplying a high voltage to an ignition plug of an internal combustion engine.
FIG. 5 is a top plan view of a conventional ignition coil; FIG. 6 is a side elevation view illustrating a state in which a high-tension cable is connected to the conventional ignition coil; and FIG. 7 is a cross-sectional view illustrating an internal configuration of the conventional ignition coil. In FIGS. 5, 6, and 7, reference numeral 1 denotes a case for accommodating a plurality of transformers; 2, a high-tension tower for forming an output terminal of each transformer; 9, a high-tension cord for introducing an output of the ignition coil to an ignition plug; and 10, a boot for sealing a high-tension connecting portion. In FIG. 7, numeral 3 denotes a core; 4, a primary winding wound around the core; 5, a secondary winding magnetically coupled to the primary winding 4 via the core 3 wound around an outer periphery of the primary winding; 6, a high-tension terminal disposed in the high-tension tower 2 connected to both ends of the secondary winding; and 8, a resin insulating and fixing the core 3, the primary winding 4, and the secondary winding 5.
Next, a description will be given of the operation. The current flowing across the primary winding 4 is energized and de-energized by an external device (not shown), and at that time a high voltage of 30 kV or thereabouts is generated in the secondary winding 5, and is introduced to an ignition plug (not shown) via the high-tension terminal 6 and the high-tension cord 9. An ignition plug corresponding to each cylinder of an internal combustion engine is connected to each high-tension terminal 6. However, in the cylinders other than the cylinders to be ignited, the pressure within the cylinders is low, so that the voltage for starting an electric discharge in the ignition plugs is appreciably lower than that for the cylinders to be ignited. Adjacent ones of the high-tension terminals 6 are insulated from each other by the high-tension towers 2 and the boots 10, and adjacent ones of the secondary windings 5 are also insulated from each other by the resin 8.
Since the conventional ignition coil in which a plurality of transformers are accommodated in a single case is arranged as described above, there has been a problem in that since a large distance needs to be provided between adjacent ones of the high-tension towers 2 in order to ensure the insulating properties of adjacent ones of the high-tension terminals 6, the size of the outside shape becomes large. In addition, there has been another problem in that, as a result of the increase in the size of the outside shape, the interval between adjacent ones of the secondary windings 5 becomes more than a dimension required for insulation, so that the amount of the resin 8 increases and the weight increases.